Schottky barrier devices are widely used in many consumer, commercial and other applications. A Schottky barrier is a potential barrier formed at a metal-semiconductor junction, which has rectifying characteristics. Many Schottky barrier devices use wide bandgap semiconductors, such as silicon carbide, gallium nitride and/or gallium arsenide, which may be used for high power, high temperature and/or microwave applications. Semiconductor Schottky barrier devices include Schottky diodes, High Electron Mobility Transistors (HEMTs) and MEtal Semiconductor Field Effect Transistors (MESFETs). A HEMT is a field effect transistor that incorporates a junction between two materials with different bandgaps (i.e., a heterojunction) as the channel, instead of a doped region, as is generally the case in integrated circuit field effect transistors. A Schottky barrier gate is used to control a two-dimensional electron gas (2DEG) between a source region and a drain region. In a MESFET, a Schottky barrier gate is used to control conduction in a channel that is formed between source and drain regions.
Nickel is frequently used for Schottky gates for gallium arsenide (GaN) HEMTs, for example, evaporated Nickel-Platinum-Gold (NiPtAu). These Ni gates commonly degrade and become leaky when the device is reverse biased. These leakages then tend to increase several orders of magnitude when stress is applied during operation, thus causing reliability issues with the device. An attempt to address the leakage problems with nickel gates is discussed in High Performance High Reliability AlGaN/GaN HEMTs by Kikkawa et al. As discussed therein, a NiPtAu structure is provided with an NiO spacer layer on the sides of the gate.